Multifocal correction providing improved quality of vision

ABSTRACT

This invention describes strategies and devices for improving the visual experience while expanding the depth of field of presbyopic and pseudophakic patients. The invention describes strategies and devices for providing improved image quality and improved visual quality of patients employing simultaneous vision bifocal, trifocal or multifocal corrections or monovision. The invention describes strategies and devices for reducing the visibility of the defocused part of the retinal image generated by simultaneous vision bifocal and multifocal ophthalmic corrections and monovision. The invention describes strategies and devices that employ control of spherical aberration or other similar asphericities to reduce the visibility of defocused ghost images. The invention describes strategies and devices that ensure that negative defocus is always coupled with negative spherical aberration (or similar asphericity), and that positive defocus is always coupled with positive SA (or similar asphericity) as a means to reduce the visibility of defocused ghost images.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure is a continuation of and claims priority to U.S. patentapplication Ser. No. 13/405,395, filed on Feb. 27, 2012, which is acontinuation of and claims priority to PCT Application No.PCT/US2010/047138, filed Aug. 30, 2010, which claims the benefit of U.S.Provisional Patent Application No. 61/238,774, filed on Sep. 1, 2009,each of which are incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to the field of ophthalmicoptical and surgical visual corrections, and more particularly providesmethods, devices, and systems for treating presbyopia and other visualconditions, and for developing prescriptions for the treatment ofpresbyopia and other visual conditions, and/or the like.

BACKGROUND ART

As the human eye ages, its ability to change its power to image objectsat different distances wanes. This decline is called “presbyopia” and itaffects all humans. A similar inability to adjust optical power of theeye's lens occurs in patients who have their natural lens replaced by anartificial lens (e.g. after cataract surgery). Thus the challenges ofseeing at multiple distances faced by presbyopes are shared bypseudophakes. Currently, there is no cure for presbyopia, and there isno perfect optical treatment that will restore this full range of visionthose skilled in the art and practice call “accommodation”. Surrogateoptical devices and strategies have been developed that are designed toincrease the range of distances that can be seen (depth of field). Suchdevices produce what is known as “pseudo-accommodation”. That is, theyincrease the depth of field without changing power of the eye itself.All of these devices and strategies are inferior to normalaccommodation, and all require compromises by the presbyopic patient.There is an obvious need to develop improved devices and strategies toenhance the vision quality of presbyopes.

There are several well-established strategies for increasing the depthof field of presbyopes. The most simple involves implementing some formof small (“pinhole”) pupil, which increases the depth of field withoutchanging the optical characteristics of the underlying optics. Such astrategy fails in low light levels and can severely limit the size ofthe visual field. More typical are strategies that actively implementsome optical lens or device that focuses light on the retina fromtargets located at different distances. One such strategy employsstandard monofocal lenses of different powers in the two eyes, called“monovision”. Most strategies, however, employ lenses that contain morethan one power, either bifocal, trifocal, or multifocal lenses.

When implemented as a spectacle lens, the different powers present inbifocals, trifocal or multifocals are distributed across the spectaclelens, and by a combination of head and eye movements, the patient canselect the region of the spectacle lens that provides a focused image onthe retina (and thus high quality vision) for targets are differentdistances. This approach, of selecting different powers by eye and headmovements will not work for soft contact lenses (CLs) or intra-ocularlenses (IOLs) or correction created in or on the cornea via refractivesurgery because the lenses or corneal corrections move with the eye.Therefore, irrespective of gaze direction, the patient is always lookingthrough the same optics.

Bifocal, Trifocal and multifocal optical corrections for presbyopes thatmove with the eye (corrections in or on the cornea (corneal inlays oronlays, other refractive surgeries), CLs and IOLs) must thereforecontain multiple optical powers within the same or adjacent regions ofthe optical device or strategy that both contribute to the retinalimage. That is, unlike the presbyopic spectacle lens correction in whichthe patient sequentially selects the physical lens location of the mostappropriate optical power, patients with presbyopic corrections in CL,IOL, or refractive surgery simultaneously employ different opticalpowers, and thus these devices and strategies are referred to as“simultaneous vision” lenses or corrections.

Herein lies the core problem faced by CL, IOL, and refractive surgerycorrections that aim to provide increased depth of field for presbyopicpatients. In addition to the light that is well focused on the retina byone of the optical powers, there is simultaneously present out of focuslight that is being imaged by the other power(s) in the simultaneousvision correction. The quality of the retinal image (and thereforevision of the patient) is, therefore, determined by this combination offocused and defocused light. Most of the ophthalmic industry's effortsto provide improved optical corrections for the presbyope have centeredon manipulating and enhancing the focused portion of this light. Theinvention described in this patent is designed to improve vision ofpresbyopes by reducing the impact of the defocused portion of the light.

The core optical characteristic of all simultaneous vision correctionsfor presbyopia is the increased depth of field provided. The primarydeterminant of the increased depth of field is the range of opticalpowers within the optical device or refractive surgery. Numerouspresbyopic corrections for presbyopes have been marketed and stillothers invented that distribute power within the lens (or refractivesurgery) using a wide range of strategies. Very simply, such opticalcorrections can be designed to have 2 powers (bifocals), three powers(trifocals), or multiple powers (multifocals). One strategy for creatinga multifocal lens is to gradually change the power of the lens from thecenter toward the edge. This can be achieved by introducing largeamounts of spherical aberration (SA) into the lens, which can eithermake the lens periphery less powerful than the lens center (negative SA,see U.S. Pat. No. 7,261,412 B2, Aug. 28, 2007 and U.S. Pat. No.0,051,876 A1, 2009). This lens would have maximum power at its center,and thus would be referred to as a “center-near” design in thatincreased power is required to focus near targets. Alternately, asimilar strategy generates a “center-distance” design by adding positiveSA to the lens (see U.S. Pat. No. 5,089,024, Feb. 18, 1992). With bothof these strategies, SA is manipulated in the lens design to increasethe range of powers present and thus increase the depth of field.

There is a different general strategy that employs discrete opticalpowers, e.g. a bifocal with two powers, or a tri-focal with threepowers, rather than a gradual change in power across the lens. In suchdesigns, the optical quality of the retinal image produced when one ofthe optics is in focus can be enhanced by including within each zone acomplete (e.g. U.S. Pat. No. 5,220,359, Jun. 15, 1993, and World Patent# WO 2005/019906 A1) or partial (e.g. U.S. Pat. No. 7,118,214, Oct. 10,2006) correction for the spherical aberration (SA) present within thehuman eye. Because the human eye typically has positive SA, these lensescorrect this by introducing negative SA. However, there may be some eyeswith negative SA, so these lenses would introduce positive SA to correctit. In many such inventions, SA is first measured using some form ofaberrometer.

When a controlled level of SA is introduced into a lens, this lens isoften described as being “aspheric”. In a third general design strategyfor simultaneous vision presbyopic corrections, SA and/or other radiallysymmetric asphericities are employed to control the transition betweenzones of different powers. That is, instead of have a spatially discretetransition, the power is gradually changed across a transition region ofthe lens. This gradual change in power is sometimes referred to as anasphericity, or SA. Several inventions employ such asphericities (e.g.U.S. Pat. No. 6,457,826 B1, World Patent WO 2007/015001 A1, World Patent# WO 0221194 A2).

Two other strategies have been implemented that employ SA or otherradially symmetric asphericities as part of a presbyopic or pseudophakiccorrection. First, contrary to the designs that employ a SA correctionwithin the different optical zones to improve focused mage quality, onecan introduce SA within the different zones with the goal of increasingthe depth of field (e.g. U.S. Pat. No. 0,176,572 A1, 2006). Also,increased depth of field can be introduced into what is designed to be amonofocal correction by adding small asphericities to the optic (U.S.Pat. No. 0,230,299 A1, 2004).

All of the above designs that employ SA or similar asphericities aredesigned to either improve the quality of the focused image within asimultaneous vision correction OR to increase the depth of field in thesame type of correction. One invention sought to employ SA control in asimultaneous vision lens to reduce the visibility of the defocused image(patent application WO 2010/014767). This strategy was simple: introducespecific SA into the bifocal correction that would correct for the eye'sSA, and thus maximize the quality of the focused portion of the light.When the focused portion of the light was indeed well focused, thisinvention claimed (with no supporting evidence) that the visibility ofthe defocused image (often referred to as a “ghost” image) would bereduced. Of course, numerous previous patents had been awarded thatalready employed SA correction within the bifocal (see above). We haveinvented a novel strategy for employing controlled SA (or similarasphericity) to minimize the visibility of the out of focus “ghost”image generated by bifocal, trifocal or multifocal presbyopic correction(see detailed description below).

DISCLOSURE OF INVENTION

Generally described, in one aspect the present invention provideslenses, design strategies, apparatuses, methods, and systems foreliminating or minimizing the visibility of ghost images present inpresbyopic corrections through the zone-specific control of the sign ofspherical aberration or other asphericity. Previous art has eithercorrected spherical aberration or indiscriminantly induced sphericalaberration without regard to the relationship between lens power andsign of SA (see above). While such approaches can be variouslysuccessful in increasing the depth of field of the presbyopic orpseudophakic eye, they produce highly visible and visually unacceptabledefocused ghost images. Such ghost images reduce the overall success ofthese presbyopic corrections. The current art is distinct from allprevious art in that either it aims to specifically couple positive SAwith the most positive powered (or least negative powered) regions ofthe bifocal and introduce negative SA into the individual optical zonewith the least positive power (or most negative power), in order tomaximize depth of field while minimizing the visibility of the ghostimage. Said in another way, our invention aims to introduce positive SAinto the near optic and negative SA into the distant optic of a bifocal,trifocal, or multifocal CL, IOL, or refractive surgery. It requiresspecifically that the distance correction and near correction containopposite sign SA to each other: negative SA in the distance correctionand positive in the near correction.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1a-c are a series of light ray diagrams depicting the focusing oflight rays from a distant object by a lens with zero (a), positive (b)and negative (c) spherical aberration (C₄ ⁰=0, >0 or <0, respectively).In each case the dotted vertical line represents the best focus plane(minimum RMS, circle of least confusion). The leftmost vertical dashedlines represent a plane closer to the lens which requires more focusingpower than the lens has and thus generates negative defocus, or negativeC₂ ⁰. The rightmost vertical dashed lines represent a plane farther fromthe lens which requires less focusing power than the lens has and thusgenerates positive defocus, or positive C₂ ⁰.

FIG. 2a-c are a series of light ray diagrams depicting the path of lightthough a lens containing no (a), positive (b), and negative (c)spherical aberration. In (b) the object is distant, while in (c) it isnear. Thus in 2(b) the C₄ ⁰ is positive, and, at the retinal plane, sois the defocus. In 2(c) the C₄ ⁰ is negative, and at the retinal plane,so is the defocus.

FIG. 3 illustrates the simulated retinal image of a high contrast letterD. Images are computed for a range of defocus levels, positive defocuson the right and negative defocus on the left. Three types of SA aremodeled: zero SA, +0.21 Deq SA and +0.50 Deq of SA.

FIG. 4 illustrates the simulated retinal image of a bifocal-correctedeye generated with same sign defocus and spherical aberration.

FIG. 5 illustrates the simulated retinal image of bifocal-corrected eyegenerated with opposite sign defocus and spherical aberration.

MODES FOR CARRYING OUT THE INVENTION

For the purposes of clearly, concisely and exactly describing exemplaryembodiments of the invention, the manner and process of making and usingthe same, and to enable the practice, making and use of the same,reference will now be made to the exemplary embodiments illustrated inthe figures and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby created, and that the invention includes andprotects such alterations and modifications to the illustratedembodiments, and such further applications of the embodimentsillustrated and described herein as would occur to one skilled in theart to which the invention relates.

Some exemplary embodiments include lenses, design strategies,apparatuses, systems and methods for simultaneous vision contact lenses,IOLs, corneal in-lays, corneal on-lays, ophthalmic surgicalprescriptions such as LASIK corrections, and other lenses or correctiveprescriptions, and the like, that employ distance and near correction incombination including all forms of monovision or variants of monovisionsometimes referred to a modified monovision. It shall be understood thatreference to simultaneous vision lenses includes the foregoing and othercorrective prescriptions. Simultaneous vision lenses include bifocal,trifocal, other multifocal lenses and the use of monofocal lensesemployed in monovision prescriptions. Certain exemplary embodimentseliminate or minimize errors in these and other simultaneous visionlenses.

Exemplary embodiments include aberration control to control thevisibility of the defocused portion of the image present in simultaneousvision lenses and monovision corrections. The defocused portion of theimage is unavoidable in exemplary simultaneous and monovision lensstrategies, and the visibility of the defocused light in the imagedetracts from the optical quality, and visual experience provided bysuch lens strategies. The visible defocused portion of the light in theimage is often referred to by patients and clinicians as a ghost imageor ghosting. The embodiments described herein include lenses, designstrategies, apparatuses, methods, and systems for eliminating orminimizing the visibility of such ghosts. Optical principles relating tosuch ghosts and reduction or elimination of such ghosts will now bedescribed in connection with FIGS. 1a, 1b, 1c, 2a, 2b , and 2 c.

FIG. 1a above depicts the focusing of light rays from a distant objectby a lens with positive power and zero spherical aberration (i.e.Zernike coefficient C₄ ⁰=0). In FIG. 1a rays are uniformly spaced inplanes of hyperopic defocus (C₂ ⁰<0) and myopic defocus (C₂ ⁰>0), whichimplies the blur circles formed in these planes are uniformlyilluminated disks of light. FIG. 1b above depicts the effect of positivespherical aberration, for which the marginal rays are refracted more andthe central rays are refracted less than in the upper diagram. Theresult is a compression of light into a pair of small high intensityblur circles in a plane of hyperopic defocus but an expansion of lightinto a larger, low intensity more uniform blur circle with indistinctedges in the plane of myopic defocus. FIG. 1c above depicts the effectof negative spherical aberration, for which the marginal rays arerefracted less and the central rays are refracted more than in the upperdiagram. The result is a compression of light into a pair of small highintensity blur circles in a plane of myopic defocus but an expansion oflight into a larger, low intensity uniform blur circle in the plane ofhyperopic defocus. The advantage of a larger, lower intensity uniformblur circle is a greater attenuation of contrast of the unwanted,defocused image produced by a bifocal contact lens. The disadvantage ofa pair of small high intensity blur circles is diplopia or annular halo,for which disturbing ghost images or haloes of high contrast are formedon the retina.

FIGS. 2a, 2b, and 2c above illustrate the optical mechanism which is thebasis for exemplary embodiments disclosed herein. Bifocal contact lensesform two retinal images of each object. One of these images will be moredefocused than the other and the intention of the present invention isto reduce the conspicuousness of the image with greater defocus byreducing its contrast and overall visibility. The ray diagrams depictonly the defocused portion of the image of a point source (e.g. rays forthe higher powered near add optic when objects are distant, and raysfrom the lower powered distance optic when objects are near). FIG. 2aabove depicts a defocused image of a distant object formed by that partof the bifocal implementing the near prescription for the case of zerospherical aberration. The eye is overpowered in this case, so defocuscoefficient C₂ ⁰>0. The blur circle on the retina is uniformlyilluminated. FIG. 2b above diagram depicts the same conditions, but fora lens with positive spherical aberration (C₄ ⁰4>0). The result is anenlarged, lower intensity, more uniformly illuminated blur circle thatde-emphasizes the blurred image by reducing its contrast. FIG. 2c abovedepicts imaging of light from a near target by the distance component ofthe prescription. Since defocus coefficient C₂ ⁰ is negative in thisexample, the sign of spherical aberration coefficient C₄ ⁰ needs to benegative to achieve the desired outcome of a large, low intensityuniformly illuminated blur circle. Note that the rationale is the sameregardless of whether the center part of the bifocal contact lensprovides the distance prescription and peripheral part of the lensprovides the near prescription, or visa versa. Positive defocus shouldbe coupled with positive SA, and vice versa.

Certain exemplary embodiments apply to all bifocal, multifocal andmonovision corrections, can be easily understood using an example of apatient employing a bifocal simultaneous vision lens. The distancecorrection within such a lens focuses a distant object, but will producedefocus when viewing a near object. Conversely, the near add power ofthe lens will focus a near object, but will produce a defocused imagewhen viewing a distant target. Certain exemplary embodiments disclosedherein eliminate or minimize the visibility of these defocused images(ghosts).

Patients using a bifocal lens or lenses may experience either positiveor negative spherical aberration (“SA”) (patients often experiencepositive SA, but some eyes, and some patients with high power negativelenses may have negative SA). Certain exemplary embodiments ensure thatthe defocused image of a near object (created the distance power of thelens), or the defocused image of a distant target (created by the addpower of the lens) will co-occur with the same sign to that of the SA.Certain embodiments provide independent control of the sphericalaberration in the distance and near optics to minimize undesired effectsof the defocused images of both distant and near targets. Someembodiments include simultaneous vision lenses which minimize visibilityof out of focus ghosts. These and other embodiments have been shown tooffer improvement in the vision correction that patients experience.

Certain exemplary embodiments include bifocal or monovison type lensesor refractive surgeries that employ opposite sign SA in the distance andnear optics. Specifically, the near add will include positive SA, whilethe distance optics will include negative SA, because the defocus causedby the near add occur due to positive defocus (excess power) whenlooking at distant target. Conversely, the distance correction willinclude negative SA because the defocus caused by the distancecorrection will be negative (insufficient power) when the target isnear. That is unlike current art which produces lenses and optics thateither have positive OR negative SA for the entire correction, orasphericities at the transitions zones, certain exemplary embodimentsensure opposite sign SA for the near and distance correction.

Some exemplary lens designs employ knowledge of patient's SphericalAberration to create bifocal/multifocal contact lens, intraocular lens(IOL) and other lens designs in which the out of focus ghost imagevisibility is minimized. Image quality in an eye corrected with asimultaneous vision bifocal can be modeled by the quality of the focusedimage and the characteristics of the defocused image which aresimultaneously present. Ocular SA can be included into the design orimplementation of this opposite sign SA invention.

Some embodiments improve simultaneous vision by improving the defocusedimage as a function of levels and types of HOAs. In FIG. 3 it can beseen that eyes with positive SA, the retinal image of an eye withpositive defocus (excess of power) is very different from the imagegenerated with negative defocus (insufficient power). The former has lowcontrast and blurred edges, and thus poor visibility, whereas the lattercan have high contrast and can be spatially distorted due to phasechanges in the image. An exemplary design goal for a simultaneous visionbifocal is to make the defocused image have low visibility. Thus, for aneye with typical levels of positive SA, the new lens design would ensurethat the near optical zone (the one defocused because of an excess inpower when viewing distance targets) would have positive SA when on theeye. Also, when the distance portion of the lens is defocused (due toinsufficient power when viewing a near target) it will have negative SAwhen on the eye. The level of SA in the eye+lens combination is the sumof that contributed by the eye and by the lens.

Using computational optics tools the inventors have generated simulatedretinal images of eyes with exemplary bifocal optics. A comparison ofthe two examples shown in FIG. 4 and FIG. 5 shows the difference inbifocal image quality when the sign of the defocus and SA are the same(FIG. 4) and when they are opposite (FIG. 5).

FIG. 4 illustrates simulated retinal image of bifocal eye generated withsame sign defocus and spherical aberration. The defocused ghosts havebeen minimized and are almost invisible. FIG. 5 illustrates simulatedretinal image of bifocal eye generated with opposite sign defocus andspherical aberration. Notice that the defocused ghosts are clearlyvisible. The visibility of the ghosts shown in FIG. 5 will be furtherincreased as the CL, IOL or refractive surgery or implant is decenteredrelative to the pupil.

Certain exemplary embodiments, by controlling the SA in the distance andnear optical zones will ensure that defocus and SA (or other similarradially symmetric asphericity) always have the same sign, and thus theghost will be invisible (or at least significantly less visible) thanwould have been achieved with opposite sign defocus and SA. This isachieved by introducing sufficient negative SA into the distancecorrection, and ensuring that there is sufficient positive SA in thenear correction. The respective negative and positive SA in the distanceand near correction is achieved when on the eye, and thus canincorporate the eye's inherent SA into the design as needed. Levels ofresulting positive and negative SA may vary from small (e.g. 0.1microns) to large (e.g. 0.4 microns) across a 6 mm diameter pupil, butcan be scaled to any pupil size and adjusted in level to achieverequired visibility of ghost images. In some instances, SA may createradially symmetric changes in optical power across the lens or pupil.Examples of SA creating symmetric changes could be Seidel SA, ZernikeSA, or any other gradual change in power as a function of the distancefrom the lens or pupil center. Such changes can be produced by shapingof the optical surface, manipulation of refractive index, andmanipulation of the zone separations and profiles in diffractivebifocals. In one embodiment, sign of this SA is defined as positive ifthe power becomes more positive with distance from the center andnegative if it the power becomes more negative with distance from thecenter.

Certain exemplary embodiments include a multifocal lens design includingreduced or minimized ghosting. Some embodiments include a contact lens.Some embodiments include an IOL. Some embodiments include an ophthalmicsurgical prescription rather than a separate corrective lens. Someembodiments include a refractive surgical correction, such as a LASIKcorrection. Some embodiments include monovision corrections and variantsof this form of prescription often referred to as modified monovision.

Certain exemplary embodiments include a method of determining amultifocal prescription including reduced or minimized ghosting. Someembodiments include a spectacle lens. Some embodiments include a contactlens. Some embodiments include an IOL. Some embodiments include anophthalmic surgical prescription rather than a separate corrective lens.Some embodiments include a LASIK prescription.

The embodiments of the invention illustrated and described in detail inthe figures and foregoing description are illustrative and not limitingor restrictive. Only the presently preferred embodiments have been shownand described and all changes and modifications that come within thescope of the invention are to be protected. It should be understood thatvarious features and aspects of the embodiments described above may notbe necessary and embodiments lacking the same are also protected. Inreading the claims, it is intended that when words such as “a,” “an,”“at least one,” or “at least one portion” are used there is no intentionto limit the claim to only one item unless specifically stated to thecontrary in the claim. When the language “at least a portion” and/or “aportion” is used the item can include a portion and/or the entire itemunless specifically stated to the contrary.

This invention is distinct from all previous inventions that eitherincrease SA or decrease SA by either introducing positive OR negative SAacross the whole pupil or an individual optical zone. It requiresspecifically that the distance correction and near correction containopposite sign SA to each other: negative SA in the distance correctionand positive SA in the near correction.

While the invention has been described with reference to preferred andexample embodiments, it will be understood by those skilled in the artthat a variety of modifications, additions and deletions are within thescope of the invention, as defined by the following claims.

What is claimed is:
 1. A multifocal diffractive ophthalmic lens,comprising: a base optic adapted to change the power of user's eye, thebase optic having a distance optical correction portion and adiffractive element comprising a near optical correction portion,wherein the distance optical correction portion provides a distancecorrection power that includes a negative spherical aberration, whereinthe near optical correction portion provides a near correction powerthat includes a positive spherical aberration of sufficient magnitude toremove ghost images that would otherwise be provided by the near opticalcorrection when viewing a distance object, and wherein the distanceoptical correction portion provides a distance correction power thatincludes a negative spherical aberration of sufficient magnitude toremove ghost images that would otherwise be provided by the distanceoptical correction when viewing a near object, wherein the near opticalcorrection portion produces only a positive spherical aberration, andwherein the distance optical correction portion produces only a negativespherical aberration.
 2. The multifocal diffractive ophthalmic lens ofclaim 1, comprising an index of refraction generating a portion of thepositive spherical aberration in the near power of the diffractive opticprofile.
 3. The multifocal diffractive ophthalmic lens of claim 1,wherein the base optic comprises a bifocal lens.
 4. The multifocaldiffractive ophthalmic lens of claim 1, wherein the base optic comprisesa trifocal lens.
 5. The multifocal diffractive ophthalmic lens of claim1, wherein the base optic comprises a lens.
 6. The multifocaldiffractive ophthalmic lens of claim 1, wherein the base optic comprisesa contact lens (CL).
 7. The multifocal diffractive ophthalmic lens ofclaim 1, wherein the base optic comprises an intraocular lens (IOL). 8.The multifocal diffractive ophthalmic lens of claim 1, wherein the baseoptic comprises a corneal in-lay.